1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device.
2. Description of the Related Art
Along with the trend to develop a liquid crystal display device of a larger size and higher resolution, display unevenness has become a problem. This results from a distortion of the scanning voltage waveform caused by the time constant of scanning lines. In other words, the scanning voltage pulse is neither deformed nor broken at the feeding end of scanning wirings, but as it departs from the feeding end, a deformation or a collapse occurs in the waveform of the scanning voltage pulse. As a result thereof, a difference arises in the field-through-voltage to be applied to each pixel when the scanning pulse is at the trailing edge, and this difference remains as a direct current (DC) component of the liquid crystal applied voltage, so that flicker (flickering) is observed. Furthermore, this DC voltage component also causes problems such as a phenomenon of residual image or smear in the display.
The technique to solve the aforementioned problem by allowing this field-through-voltage to become equal within the screen is proposed in JP10(1998)-39328A. FIG. 36 and FIGS. 37A-37C show the configuration thereof. FIG. 36 is a plan view of a liquid crystal display device, wherein 211 is a liquid crystal panel, 212 is a driving circuit on the scanning side, and 213 is a driving circuit on the image signal side. FIGS. 37A-37C are enlarged views showing the pixel part in portions a, b and c of FIG. 36 respectively. With respect to the area of overlapping portions 210a-210c between an auxiliary capacity line 204 disposed under an interlayer insulating film and a pixel electrode 203, the part of the overlapping portion 210a is set to be larger than the part of the overlapping portion 210b, and the part of overlapping portion 210c is set to be smaller than the part of the overlapping portion 210b. As a result, as it departs from the feeding end of the scanning wirings, the storage capacity formed in the aforementioned overlapping portions is reduced, and thus, it is described that the difference in the field-through-voltage accompanied by a deformation or a collapse of the scanning voltage waveform can be eliminated. Moreover, by forming the auxiliary capacity line 204 with the use of a transparent electrode, it is described that the area of the light transmitting through the a portion, the b portion and the c portion can be made equal.
However, since a signal delay occurs when a resistance of the auxiliary capacity line is high, a metal film with a low resistance generally is used. Due to the fact that the metal film used here is an opaque body, a difference in the area of the common electrode leads to a difference in the aperture ratio for each pixel in such a configuration. When the difference in the aperture ratio is to be eliminated by a light shield film 205 as shown in FIGS. 38A-38C, a bonding margin of the substrates needs to be taken into consideration, so that the aperture ratio drops drastically.
Furthermore, when the aforementioned configuration is applied to a lateral electric field type (e.g., IPS-type: In-Plane Switching type) liquid crystal display device or the like, in which an area which is not covered with a pixel electrode is included in a part of the pixel, a change in the area of the capacitive accumulation portion disturbs the electric fields applied to the liquid crystal layer. As a result, problems such as deterioration of display characteristics or a difference in the display characteristics for each pixel occur.
To solve the aforementioned problems, an active matrix liquid crystal display device of the present invention is an active matrix liquid crystal display device comprising a capacitive accumulation portion formed by overlapping a pixel electrode, an insulating layer and a common electrode for each pixel area, and a non-electrode area in a part of the pixel area which is not covered with a pixel electrode. The liquid crystal display device is characterized in that a peripheral shape of said capacitive accumulation portion on a side contacting said non-electrode area is substantially the same between the respective pixels, and that a value of a storage capacity in said capacitive accumulation portion differs on a feeding side and on a termination side, and also that the value on the feeding side is larger than the value on the termination side.
In the aforementioned device, xe2x80x9csubstantially the samexe2x80x9d means that a difference to the extent of the permissible quality variation during manufacturing is included herein.
According to this structure, the aperture ratio and the electric fields in the vicinity of the liquid crystal display area can be maintained substantially constant independently of the pixel, and a uniform display is possible from the termination side to the feeding side.